The present invention relates generally to fluid dispensing apparatuses, and more particularly to a volumetric, pistonless fluid dispensing apparatus having no moving parts in contact with the fluid.
Numerous types of fluid dispensing apparatuses exist for filling bottles. One type of fluid dispensing apparatus which is in widespread use is positive displacement fillers. Positive displacement fillers typically include moving parts which contact and displace the fluid being dispensed. For example, one type of positive displacement filler uses a piston and cylinder arrangement. In this type of positive displacement filler, the backward movement of the piston draws fluid into the cylinder through an inlet port, and the forward movement of the piston expels the fluid through an outlet port. Another type of positive displacement filler uses a rotary pump to move the fluid.
Positive displacement pumps have gained widespread use in the United States for two reasons. First, positive displacement pumps can operate at relatively high speeds, filling as many as six hundred bottles per minute. Additionally, positive displacement pumps are accurate up to about .+-.0.5%. However, there are distinct disadvantages associated with positive displacement pumps.
One disadvantage with positive displacement fillers is that the fluid comes into contact with moving parts. As the moving parts wear, particulate matter enters the fluid causing particulate contamination. If severe enough, particulate contamination can render the product unusable.
Another important disadvantage with positive displacement fillers involves the difficulty in cleaning and sterilizing the moving parts in contact with the fluid. In positive displacement pumps, the critical tolerances between parts, such as the piston and cylinder, precludes effective cleaning in place. Thus, the user must disassemble the apparatus for cleaning and sterilization. This process is not only time consuming, but may result in biological contamination of the parts when they are handled by the mechanic during reassembly.
Another type of fluid dispensing apparatus is the time/pressure filler. Generally speaking, the time/pressure filler includes a fluid chamber which is maintained under a relatively constant pressure. The fluid is dispensed from the chamber through a compressible line. Fluid flow is shut off by a pinch type valve which squeezes and collapses the discharge line. A pre-determined volume of fluid is dispensed by opening the discharge line for a pre-determined period of time and then closing the line. If the pressure within the fluid chamber is maintained constant, an equal amount of fluid should be dispensed each time the cycle is repeated. However, time/pressure fillers do not work as well in practice as they do in theory.
The primary difficulty with the time/pressure filling apparatuses is that the tubing is deformed to shut off fluid flow and does not always return to its undeformed state immediately, particularly when the apparatus has been sitting idle for a long period of time. Thus, the critical orifice through which the fluid is dispensed may vary somewhat from the fully open line. The variance in the critical orifice will cause the fluid flow through the discharge line to vary until the discharge line returns to its undeformed condition. As a result, time/pressure fillers will be less accurate during the first few filling cycles.
Based on the foregoing, it is apparent that a need exists for a dispensing apparatus which achieves the same, or better degree of accuracy, as positive displacement fillers without moving parts coming into contact with the fluid.